These are two specific aims of the research that has been supported by RCMI funds. The first is an elucidation of the structure and function of repetitive DNA with special attention on heterochromatin. Heterochromatin has generally been referred to as inert DNA, but actually plays a critical role in chromo- some behavior during meiosis and mitosis, making it an essential part of the genome. The second aim is to identify the genetic basis of two inherited diseases, hypertension and keloids, that have a higher incidence in populations of African descent than in Caucasian populations. These diseases are part of a class of disorders that are more common in African-Americans and other populations of African decent called fibroproliferative diseases.